Local area networks (LANs) are prevalent in computing, and the connection of computers in a LAN provides a convenient vehicle for distributed processing and efficient allocation of resources, such as servers, printers, scanners, and gateway communication devices. In the office environment, LANs typically comprise wired interconnections between stations or computers. Wired LANs have the disadvantage that extensive cabling is required to interconnect the stations in the network. The installation of such cabling is generally inconvenient and gives rise to inflexibility if it is desired to alter the physical locations of the stations comprising the network.
To overcome the disadvantages of wired LANs, it has been proposed to utilize a wireless transmission link to replace the cabling connections of a wired LAN. Wireless communication between two points is well known and two approaches have emerged as solutions for wireless LANs. One solution uses radio frequency (RF) communication techniques to implement the communication channels. The other solution utilizes infrared (IR) radiation as a communication medium. Infrared based systems have found widespread appeal, particularly in an indoor environment, such as an office building. Infrared based systems have the additional advantage of not requiring compliance with the more stringent government regulations applied to RF based systems, for example, as would be required for a system utilizing microwave frequency signals.
Communication interconnections in a wireless LAN utilizing infrared are set up using infrared transceivers. A station, e.g. personal computer (PC), is connected to a transceiver. The transceiver has an infrared transmitter and an infrared receiver. The infrared transmitter includes at least one infrared light emitting diode (LED), and typically comprises an array of infrared LEDs. The infrared receiver comprises one or more photodiodes responsive to the output wavelength spectrum of the LED in the transceiver of the communication station on the LAN.
In the art, infrared-based transceivers fall into two general classes: diffused IR transceivers and directed beam IR transceivers. Diffused IR transceivers typically comprise an array of LEDs which disperse infrared beams throughout an office space. The infrared beams are picked up by the receivers of transceivers on stations located throughout the office. Diffused IR transceivers permit a data processing station, i.e. computer, to talk with a number of other stations located in the office space. In directed beam IR transceivers, the infrared beam is directed towards the transceiver of the station intended for communication. In other words, there is a line of sight path between two stations and the infrared beam is directed along this line of sight path. Direct beam IR transceivers are commonly referred to as "point and shoot" or "serial IR" systems, and find widespread use in establishing a communication link between a computer and peripheral device, for example, a notebook computer and a laser printer.
The performance and integrity of an infrared communication link will depend on the operating environment, particularly the ambient light and the reflectivity of the interior surfaces. Infrared systems tend to provide better performance in an office space where the ambient light level is not very high, especially, in systems where the carrier beam is not high frequency modulated. The reflectivity of the interior surfaces of an office space will also affect transmission of infrared beams. Surfaces having a tendency to absorb infrared beams will degrade the performance of an infrared communication system, and in particular a system comprising diffused beam devices. It is possible to lessen the effects of the operating environment using set-up techniques for the infrared transceivers and adjustments to the orientations of the beam paths.
The development of reduced size laptop, notebook computers and handheld computing devices has necessitated the concurrent development of modems and network adapters of suitable size to fit within the housings of these computers to provide the capability for connection to LANs.
This trend has led to the development of PCMCIA (Personal Computer Memory Card International Association) cards to house the interface circuits. PCMCIA cards are also known as PC cards in the industry. These cards are inserted into slots provided in the computer housing and provide an interface between the external communication line and the computer. The PC cards come in two standard sizes. Type I PC cards are 3.3 mm thick, and Type II cards are 5 mm thick.
With the development of wireless LANs there is a need to provide an infrared optical transceiver for a PCMCIA application interface card for use with laptop and notebook computers and handheld computing devices.